Interference neutralizer for alternating-current telegraph systems



.Patented Apr. l, l1930 UNITED lSTATI-:sf PATENT- @Price LEO A. KELLEY, F ELMHURST, NEW YORK, ASSIGNOR TO AMERICAN .TELEPHONE AND TELEGRAPH COMPANY, A- CORPORATION 0F NEW YORK INTERFERENCE NEUTRALIZER FOR ALTERNATING-CURRENT TELEGRAPH SYSTEMS Application led January 241930. Serial No. 423,218.

This invention relates to alternating current telegraph systems, and particularly to means for neutralizing the effect of extraneous interference upon the receiving apparatus 6 of such systems.

10 is used to operate a polar relay. This relay normally has a biasing winding through which a current flows steadily of such a value that it neutralizes approximately` one-half of the effect of the normal operating current when both currents are iiowing. This causes the armature to be moved from one contact to the other with equal force in either direction, as the operating current is alternately on 4and off. 4Interfering currents set up in the line circuit by sources extraneous to the system itself often cause false operation of the relay, and also produce distortion of the carrier current signalsy being transmitted over the line by such interference with the operation of the receiving relay.

' My invention resides in a system for neutralizing interference in an alternating current telegraph system by a method that consists in applying to the polar receiving relay a neutralizing impulse whose magnitude is equal to or greater than the disturbance in the signaling channel, and controlling the ,time and the direction of application of the said neutralizing impulse so that it will be effective to prevent the disturbance in th signaling channel from moving the armature ofthe receiving relay from one of the contacts, for example, the spacing contact of'the said relay if it is desired to protect against interruptions to spacing signals. Protection against interruptions to marking signals may be eected by slightly changing the circuit connections in a manner that will be set forth hereinafter. The arrangement disclosedpin the copending application of Kelley, Monk and Thorp, Serial No. 836,884, filed February 1, 1929, provides for the automatic'control of the application of the neutralizing impulse, by andin accordance with the received signaling impulses, so as to automaticallyneutralize the effectupon said relay of interference received in the signaling chan.

nel during the reception of marking impulses as well as during the reception of spacing impulses, and, to that extent constitutes an improvement upon my invention which' will now be fully described. This invention will be clearly understood from the following description when read in connection with the attached drawing, of which Fig. 1 shows schematically a simple form of embodiment of the'invention for 'neutralizing,interference during the reception of a spacing impulse; and Fig. 2 shows the manner in'which a portion-of the circuit vof Fig. 1 is modified in order to effect neutialization of interference during the reception of marking impulses.

In the drawing the line L represents a transmission circuit or medium o ver or through which a plurality of carrier frequencies such as' f1, f2, etc., may be transmitted from the carrier transmitting apparatus 1 to the carrier receiving apparatus connected with the other end of the said line. The receiving station comprises a plurality of branch circuits A. B, C, and D. Circuits A and C are intended to -receive the signaling channels based upon the carrier frequencies f1 and f2, respectively. Circuit B serves as a neutralizing channel in connection with lcircuit A, and in like manner circuit D serves as a neutralizing channel in connection with circuit C. Only two of the branch circuits, namely, A and B, are shown in their entirety -since the other pairs of signaling and neu-ir tralizing circuits are preferably similar to A and B. The circuit A has connected therewith a selecting circuit or network2 which may be a tuned circuit, filter, or vother selective device to permit the passagel of the frequency 7", or a band based upon that frequency. The output ofthe selecting circuit 2 -is connected with an amplifier 8 which may be ofaiiy well known type, and the latter is connected with the rectifier 4, shown as of the 'vacuum tube type. The grid circuit of the rectifier contains a battery 5 .that is designed to apply a negative bias to the grid of such magnitude as to suppress the space ice.

current when signals are not being received. The plate circuit of the rectifier is connected with the winding 6 of the polar receiving relay 7, which winding is also connected with the source of plate voltage 8. The polar receiving relay has also two other windings .9 and 10. Winding 9, which is the biasing winding is so poled and the magnitude of the current flowing therethrough from the source 8 is such as to tend'to keep the armature 11 upon its spacing contact when current is not flowing through winding 6. Winding 10, which constitutes the neutraliz- -ing winding of the relay, is connected between the source of Voltage 8 and the armature 12 of relay 13. The upper contact of relay 13 is connected with the plate of thel rectier- 14 associated with the neutralizing circuit B. vrIhe mode of connection of the plate of rectifier 14 and the contact of relay 13, and the direction of flow of current through the winding 10, as shown in the drawing, will neutralize interference that occurs during the reception of a spacing impulse; that is to say, the circuit arrangement.

shown in the figure will prevent the movement of the armature 11 from its spacingA contact in the event that an interfering impulse comes into the circuit A during the time interval representing the reception of a spacing impulse. Later, I will show the manner in .which` the circuit connections should be made to prevent the/'movement of the armature 11 from its marking' contact when interference enters the circuit Av during the reception of a marking impulse.

The contacts of the polar relay 7 are connectedwith the marking and spacing batteries 15 and 16, respectively. The armature 11 is connected with the winding of relay 13 which is inturn connected with the loop circuit L1 having a telegraph substation connected therewith, represented diagrammatically by the relay 17 and the battery 18. The polarity of the said batteries is as indicated upon the drawing; The neutralizing circuit B contains a selecting circuit 19, an amplifier 20, and the rectifier 14, the latter having a negative biasing source 21 connected with the grid, the magnitude of which is such as to suppress space current in the rectifier 14 when no disturbing impulses are being passed by the network 19 from the line to the rectifier 14.

In carrier telegraph systems, a'marking impulse consists of a train of oscillations of the carrier frequency, and a spacing impulse represents the absence orsuppression of such in the said line. Since the carrier current is not transmitted during the spacing interval, no space current will flow in the rectifier 4 because the negative bias produced upon the grid by the battery 5 is suiiicient to suppress such space current. Accordingly, current will not flow in the winding 6 of relay 7 and the armature 11 of that relay will be held against its spacing contact by virtue of the current flowing through the biasing winding 9. Furthermore, since battery 16 is equal to, and opposes battery 18, no current will iow through the winding of relay 13 which is connected in series with batteries 16 and 18 and the loop L1. Consequently, relay 13 will be deenergized and its armature 12 will rest against its upper contact, which will establish a connection from the grounded battery 8, through winding 10, armature 12, and upper contact of relay 13, to the plate of rectifier 14, but no current will flow through the neutralizing winding 10, because the negative bias maintained upon the grid of 14 by the battery 21- is sufficient to prevent the, flow of current from the plate to the filament of 14, when no interfering currents exist in the line, which was the condition assumed just above.

If a disturbance occurs in the vicinity of the line L, it will tend to produce therein an interfering current of a plurality of frequencies, some of which may be of the same frequencies as the carrier currents, or within the range ofthe bands based upon the said carrier frequencies f1, f2, etc., and another or others of said interfering frequencies may be outside said range of carrier frequencies. Thev flow is to energize the said winding'and to tend toj cause the armature 11 to move from its spacing contact, which tendency, if unchecked, would interfere with the reception of the spacing impulse of thesignal being transmitted. That effect is, however, prevented by utilizing the portion of the disturbance that lies in the frequency range of the selecting circuit 19 ofl the neutralizing circuit B, which frequency range may lie within the range of the group of channels employed in transmission over the system, 0r outside the range of said group. That portion of the disturbance that passes through 19, which will be designated the neutralizing impulse, will be amplified by 20 and iinpressed upon the grid of the rectifier 14, thereby overcoming the negative bias of 21. Accordingly, current willl flow through the plate circuit of the rectifier 14 which in cludes the winding 10 of the polar relay, and

the upper contact of relay 13, whichcontact ing the receipt of a spacing signal impulse.

Since the effect of the flow of current through the winding 10, due to the neutralizing im'- pulse, is opposite that of the flow of current through Winding 6, due to the interfering impulse, that lies in the frequency range of the signaling channel, it Will be apparent, that by controlling the magnitude of the space current of the rectifier 14, (by adjustment of the amplifier 20, or otherwise), so that the current in Winding 10 may be made equal to or greater'than the effect of the space current of rectifier l that flows through Winding.

6, the armature 11.of the polar receiving relay 7 Will be prevented from leaving its spacing contactduring the reception of a spacing impulse, regardless of thc presence in thev line of an interfering current of the same frequencyas that employed in the signaling channel.

Fig. 2 shows the manner in which the circuit of Fig. 1 may be readily arranged to neutralize such interference as arises during the .reception of a marking impulse. To accomplish that result the plate conductor 22 of the rectifier 14 is connectedvwith the lower contact of relay 13 and, furthermore,vvinding 10 is so connected between armature 12 and the source of voltage 8 that the direction of flow of the current through the said winding is lthe reverse of that shown in Fig. 1. As arranged in Fig. 2, current will flow through Winding 10 Whenever interference occurs during the reception of a marking impulse, andthe direction of flow of the current through Winding 10 Will be such as to assist in keeping the armature 11 of receiving relay 7 upon its marking contact.

I have described the mode of arranging the circuit to render the receiving relay unaffected by interference during the time vof reception of either a spacing impulse or av marking impulse. From a practical standpoint it is more desirable to neutralize interference during the spacing interval because the circuit is more susceptible to interference during that interval than during the recepti0n\ of markingimpulses. Furthermore, the

marking interference -may be substantially reduced, by designingthe rectifier input circuit of the signal channel to make it less susceptible to such interference.

While this invention hasl been described as embodied in a particular form, it is to .be understood that such showing is purely illustrativevinasmuch as the invention isv capable of embodiment in other forms Without departing from thespirit'and scopeof the appended claims.

Whatis claimed is:

1. The method of neutralizing interference in an'alternating current telegraph receiving system, in Which the normal movement of the .armature of a' receiving relay from one contact to another is controlled by rectified signaling currents representing marking and spacing impulses, which consists in transmitting a slgnal over or through a medium by' means of a carrier frequency, Which signal is exposed to interference from a source of disturbances, selecting and rectifying the said carrier frequency, and impressing the rectified current upon the receiving relay, also selecting and rectifying a portion of the disturbance having a frequenc tdifferent from that used for the said signal, applying said rectified disturbance to the said receiving relay, and controlling the application of the said rectified disturbance by the received signal impulse to be protected against interference, so that the rectified vdisturbance Will prevent the interference existing in the sig-` naling' channel from moving the armature of the receiving relay from that contact 4to Which it has been moved by the signal impulse to be protected against interference.

2. The method of neutralizing interference in an alternating current telegraph receiving system, in which the normal movement. of the armature of a receivingrelay from one contact to another is controlled by rectified signaling currents representing marking and spacing impulses, which consists in transmitting a signal over or through a mesesl dium bymeans of a carrier frequency, which v signal is exposed to interference from a source of disturbances, selecting the current of the band based upon the said carrier, rectifying that current, likewise selecting the current resulting from interference whose frequency lies outside the said band, rectifying that current, applying both rectifiedv currents to the receiving relay normall responsive to the signal being received, and? controlling the 'time of application of the rectifiedI interfering current ofthe said different frequency so that it Will be effective to keep the armature of the receiving relay upon that contactto which it has been moved by the signal impulse to he protected against interference.

3. rI`he method for neutralizing interference i-n 4an alternating telegraphreceiving system, in which the normal movement of the armature of a receiving relay from one contact to another is controlled by rectified signaling currents representing marking and loo spacingimpulses, Which consists in transmitl ricr frequencies, separating the carrier channels bythe process of frequency selection, rec` tifying the selected carriers and the interference currents of the same frequencies as the said carriers, simultaneously selecting and rectifying an interference frequency or frequencies, differing from the frequencies employe-d in the carrier channels, to form a neutralizing current to overcomel the eEect of any interference existing in the carrier channels, and controlling the application ofthe said neutralizing current to the receiving ref lay by that received signal impulse'that is to be .protected against interference, so that the neutralizing impulse will prevent the interfering impulse that lies within the range of a carrier channel from moving the armature of the receiving relay from that contact to which it has been moved by the particular signal impulse to be protected.

4. In a system for neutralizing interference in analternating current telegraph receiving system, the combination with a source of signals of a plurality of carrier currents of dierent frequencies for transmitting the said signals over or through a medium that is eX- pose-d to atmospheric disturbances, a plurality of signal receiving circuits each having means to select from the said medium the current within a band based upon one of said frequencies, which current may ,result from either the signal or from disturbances whose frequency comes within that of the band, means to rectify the selected currents, one or more neutralizing circuits to pick up from said medium disturbances of a lfrequency or frequencies lying either between adjacent bands, or outside the range of the group of bands', a receiving relay effectively connected with two of said rectiiiers, one associated with a. signal receiving circuit and the other with a neutralizing circuit, and means controlled4 bythe received signal impulses adapted to..

close the connection between the said rectifier of the neutralizing circuit, and the said receiving relay whenever the receiving relay is energized by the particular signal impulse that is to be protected against interference.

5. In a system for neutralizing interference in an alternating current telegraph receiving system, the combination with a source of signals of a source of current of a carrier frequency for transmitting the said signals over or through a medium that is exposed to at-l mospheric disturbances capable of setting up interfering frequencies lying within and also without the band of frequencies represented by the signal modulated carrier, a signal receiving circuit having means to select from .the said medium the current of the frequen- January, 1930.

LEO A. KELLEY. 

